Simultaneous measurements of (p~l) and of the molar volume are reported for liquid mixtures of 3He in 4He over the temperature range between 0.5 and 2.5 K. Here ~q is the shear viscosity and p is the mass density. In the superfluid phase, the product of the normal components, Pn and ~n, is measured. The mixtures with 3He molefractions 0.30 < X < 0.80 are studied with emphasis on the region near the superfluid transition T~ and near the phase-separation curve. Along the latter, they are compared with data by Lai and KitChens. For X > 0.5, the viscosity singularity near Tx becomes a faint peak, which however fades into the temperature-dependent background viscosity as X tends to the tricritical concentration Xt. Likewise, no singularity in 7 I is apparent when Tt is approached along the phase separation branches o-_ and or+. Furthermore, viscosity data are reported for 3He and compared with previous work. Finally, for dilute mixtures with 0.01 -< X -< 0.05, the results for 71 are compared with previous data and with predictions.

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A torsional oscillator cell is described, by means of which simultaneous precision measurements of (prl) and of the molar volume can be made in liquid 4He-4He mixtures over the temperature range between 0.5 and 3 K. Here p is the mass density, rl the shear viscosity and in the superfluid phase they become the contributions p, and qn of the normal component. The results of ;l for 4He near the superfluid transition are compared with the predictions by Schloms, Pankert and Dohm, and by Ferrell. Measurements of (P~l) are reported for mixtures with 0.64 < X < O. 74, where X is the 3He mole fraction. Those for X =0.67 and 0.70 are compared with data by Lai and Kitchens. The viscosity experiments show no evidence of a weak singularity at the tricritical point.